CNC Routers: Five tips for getting the best cut

by | 27 May 2020 12:16 pm

By Susan Mattine

Learning how to customize and configure a computer numerical control (CNC) router for the first time can be a time-consuming and confusing process. Watching small pieces fly off the machine or fabricating parts with rough edges are common issues for novice users. Workarounds or makeshift solutions might be a temporary answer, but what about in the long run? In these cases, it is important to seek assistance from a reputable CNC manufacturer for technical guidance. Vendors often attend trade shows, hold open houses, and give live demonstrations on their machines. Watching a CNC router in action is a great introduction to manufacturing automation. When one is ready to invest in this equipment, it is a good idea to choose a vendor that offers training and post-sales service. These are the vendors signmakers can trust to help take their sign and graphics business to the next level.

In the meantime, it is important one conducts the proper research to become familiarized with all things CNC-related. When one is all set to go, the following five tips for successful CNC routing should be considered.

1. Purchase a CNC hybrid to maximize versatility

CNC hybrids are becoming increasingly popular as a niche technology because of their versatility. For instance, one can produce dimensional signage one day, acrylic letters the next morning, and print-to-cut graphics that afternoon—all on the same machine.

The key to this versatility is in the design and engineering of hybrids, which can accommodate both standard router bits that are typically used for hard materials and knife cutters for softer ones. With only minimal set-up time, the router itself can switch from one type of cutter to another, after being programmed.

Installing a CNC hybrid can make a lot of sense for sign companies, particularly smaller shops where floor space is at a premium, and capital expenditures are made with utmost caution.

2. Preserve tool life by implementing a two-part cutting process

Experienced CNC machinists often split the cutting process into two parts—a roughing cut and a finishing cut—each completed using a different tool. This preserves the finishing tool longer, which in turn enables a higher quality finish. For instance, this technique should be used when cutting acrylic for retail or other type of display work, as it is critical to achieving the best edge while preserving tool life. Time is also saved on each project as the finishing tool does not need to be changed. To further maximize tool life, a polycrystalline diamond (PCD) tool may be used, which can easily achieve two to three times the tool life of regular carbide tools.

The roughing cut does the majority of the work, reducing the load on the finishing cut. The roughing pass churns out most of the material, whereas the newer finishing cutter removes the remaining material and leaves a smooth, polished edge.

When creating the program for the rough cut, approximately 0.58 mm (0.02 in.) should be left on the ‘Z’ axis to prevent the router from fully cutting through the material, leaving the part held in place. Also, the tool should be offset with an additional allowance of approximately 0.23 mm (0.008 in.) around the profile. By doing this, it leaves only a very small amount of material for the finishing tool to remove. This also reduces cutter loading, chip volume, as well as minimizing the chances of vibration spoiling the edge finish. The CNC router’s cut speed should be set to approximately 1.5 m/min (60 in./min), and the material should be cut in a ‘climb’ or clockwise direction.

The finishing pass, which cuts all the way through the material, concludes this process. To perform this pass, the profile allowance should be removed, and the cut speed should be reduced to about 1 m/min (40 in./min), cutting in the same direction. The finishing pass should produce little if any noise (the higher the noise is, it will result in a rougher cut). If the noise increases at any point during the finishing pass, the operator should stop the machine to check the work and reassess the situation. In some cases, one may need to reduce the feed speed or acceleration rate, or possibly even fit a new tool.

If the quality of the completed job starts to diminish, one should consider replacing the finishing tool. This will need to be changed on a regular basis to maintain the highest quality.

3. Regularly inspect and clean the vacuum table to minimize movement

Before one starts cutting, they should take a good look at the router deck to make sure it is free of dust and chips. If not, it should be cleaned. If chips and dust are present, it may prevent the part from lying flat on the sacrificial bed. If the part is not flat, the vacuum hold is reduced. Other steps one should follow include:

• Use a sacrificial bed/spoil board. A sacrificial bed, also known as a spoil board, is a disposable surface placed on top of the router to protect it from damage. Typically, medium-density fibreboard (MDF) is used. As it is a porous material, it allows air to flow through it to the vacuum pump.
• Examine the sacrificial bed. Visually inspect the sacrificial bed to determine if there is an overabundance of cutter marks, which can cause vacuum bleed. If so, it may be time to either replace the bed (which should be done approximately every six months) or skim the bed’s surface.
• Skim the sacrificial bed regularly. A clean, smooth surface is vital for effective material hold down. To maintain this surface, it is necessary to frequently skim the bed using a skimming tool. A general rule of thumb is to skim the bed at the beginning of each week.
• Check for plumbing leaks. If everything else appears okay (that is, there is a clean bed with no significant cutting marks) and there is still vacuum loss, check the pipework connecting the vacuum pump. Leaks will reduce the effectiveness of the vacuum hold.

4. Use different cutters for different materials for a high-quality edge finish

While a cutter may work well with one type of material, it might not always be the best choice for others. In fact, there are cutters specifically designed for certain materials. Typically, these cutters last longer and perform more effectively than general purpose cutters.

The main issue with using a cutter that is not specifically designed for use with the material one is working with is in the quality of the edge cut. If one is working on a display project that will be in a highly visible place, it is important to achieve a smooth, clean, and shiny edge versus one that is frosty, untidy, and rough. For example, when working with acrylic, if the wrong tool is used, the cut may result in a rough finish with ripple marks. The modifications in specifically designed cutters can make a substantial difference in the cut quality.

That said, it is a good idea for signmakers to talk to their CNC router supplier for advice and expertise on which tool to choose for a particular project. If the supplier has a local presence, one should visit the office and ask the supplier to test the material in question with several tools to determine the best one for the job.

5. Keep a maintenance schedule

An important part of creating a cutting strategy is to ensure regular maintenance checks are conducted on one’s CNC router equipment. By keeping a maintenance log, following a schedule, and sticking to it, signmakers can ensure trouble-free operation. The following inspection checks should be reviewed as a way to extend the life of a CNC router and tools for many years to come.

• Clean it regularly. Any buildup of fluids or chips can easily get into the bearings and controls—this can be a sure recipe for problems if not corrected every day.
• Change filters. Although there is no standardized schedule (it depends on the specific machine), all filters should be checked weekly and changed as needed.
• Lubricate. The nice thing about routers is that despite all their parts, they do not require extensive lubrication. Bearings, pumps, and oscillating knives need regular lubrication, but this will vary from one machine to the next.
• Air supply cleaning. Most CNC routers operate with pneumatic air that has to be clean, dry, and maintained at a steady pressure (more than 80 pounds per square inch [psi] or 6 barometric). Damage to the machine is likely in a very short time frame due to incorrect specifications; therefore, pressure should be checked regularly.
• A safe and proper power supply. The power must be sufficient and safely connected as required by local utility regulations. Machine failure is likely to occur in cases of poor electrical grounding, low voltage, or insufficient capacity. As is the case with every computer-operated mechanism, power spikes will cause serious damage.

 

Common issues

For those signmakers who are still not getting the results they expect, the following are some common causes to check:

• Over-tightened collet;
• Incorrect feed rate (finishing pass);
• Incorrect spindle speed (finishing pass);
• Wrong type of material (extruded not cast); and
• Wrong cutter.

Following these tips can help one optimize their routing experience and keep their machine working at high capacity for many years to come. There is a wealth of knowledge out there to tap into; therefore, signmakers should take the time to partner with an experienced CNC machine supplier. Selecting the right tools, materials, and options makes a world of difference—especially when turning an ordinary project into an innovative product that will make one’s business stand out from the competition.

Susan Mattine is the communications and public relations associate for AXYZ Automation Group, a global leading manufacturer of tailored cutting solutions. She can be reached via email at smattine@axyz.com[5]. For more information, visit www.axyz.com[6].

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